1. Field of the Invention
The present invention relates to a semiconductor device and a manufacturing method thereof, and more particularly, to a semiconductor device and a manufacturing method thereof that uses lasers with different scanning directions in an annealing process to reduce thermal damage caused by the annealing process.
2. Description of the Prior Art
In the process of fabricating a semiconductor device, different dopants can be implanted in the semiconductor substrate in order to control the number of charge carriers. Different doped regions are thereby formed in the semiconductor device. For a variety of doping methods, such as ion implantation processing, liquid deposition processing, thermal diffusion processing, or chemical vapor deposition processing etc., an annealing process is required after the doped regions are formed in the semiconductor substrate. This relieves damage caused by the doping process and also activates dopants within the semiconductor substrate, which helps to reduce the resistance values of these dopants.
With the decreasing sizes of semiconductor devices and correspondingly increasing densities, doped regions have to achieve a higher quality standard. Therefore, annealing processes have to be completed in a shorter time. Conventionally, a rapid thermal process (RTP) is performed on semiconductor substrates for annealing. In the rapid thermal process, wafers are heated by an external heating source, such as tungsten lamps or halogen lamps etc. Laser annealing techniques have been considered to replace the rapid thermal process. Since a laser is capable of completing the annealing process in an extremely short time, the laser annealing process can advantageously form doped regions with shallower depths, so that the electrical performances of semiconductor devices can be improved.
In the laser annealing process, however, a high density power is imposed by the laser on the upper surface of a semiconductor substrate. As many devices made of different materials and having different layouts with different patterned densities are disposed on the upper surfaces of the semiconductor substrate, the laser annealing process may cause a temperature gradient along the longitudinal direction of the semiconductor substrate, leading to defects in the semiconductor substrate.